Both had pantheons of deities, so the Greeks actually were polytheistic. However, India was in relative isolation compared to Greece insofar as the expansion by conquest of the Roman Republic, then Empire, went. Therefore, it was relatively early on that Greece fell under the dominion and domination of Rome. In due time, Christianity (the world second major monotheistic religion, took hold in Rome until it, and monotheism, supplanted polytheism there. India in the meanwhile remained isolated both by language and culture as well as by distance; so outside influences were impeded from having much influence on developments of a religious nature. In the twentieth century, India was able to avert encroachment of monotheism in the form of Islam, but only at the cost of bloody wars and sectoring of the country to form Pakistan and Bangladesh.
